Re-evaluation of the fludrocortisone test: duration, NaCl supplementation and cut-off limits for aldosterone.
OBJECTIVE
Primary aldosteronism (PA) is the most common form of secondary hypertension. Thus, the aims of this study were: (1) to clarify whether the fludrocortisone suppression test (FST), which confirms autonomous aldosterone secretion, is reliable when carried out during a shorter period of time and (2) to confirm the importance of NaCl supplementation. The cut-off limits already obtained for aldosterone in healthy subjects during the FST were applied in hypertensive patients with a high aldosterone to renin ratio (ARR).


METHODS
The healthy subjects were allocated to three groups. Fludrocortisone was administered 4 times daily over 4 days and sodium chloride was supplemented in 3 different doses. The result was applied in 24 hypertensive patients, in 24 healthy subjects (10 women (23-38 years old) and 14 men (23-58 years old)) and in 24 patients with hypertension and high ARR (16 women (45-74 years old) and 8 men (56-73 years old)). Blood pressure, aldosterone, renin, potassium and sodium were measured.


RESULTS
After three days of FST, there was a significant decrease in the serum level of aldosterone in the healthy subjects, regardless of high or low sodium chloride supplementation (p<0.001). The decrease in serum aldosterone was significantly less pronounced in patients with PA than in healthy subjects and hypertensive patients without PA (p<0.001). The 95th percentile of plasma aldosterone at the end of the test was 225 pmol/L.


CONCLUSIONS
The FST can be shortened to 3 days and a daily 500 mg NaCl supplementation is sufficient. A cut-off value for aldosterone of 225 pmol/L after 4 days with FST is appropriate.
Westerdahl
Christina
C
Department of General Practice, Lund University, Lund, Sweden. cwesterdahl@telia.com
Bergenfelz
Anders
A
Larsson
Johanna
J
Nerbrand
Christina
C
Valdemarsson
Stig
S
Wihl
Anders
A
Isaksson
Anders
A
D000328:Adult; D000450:Aldosterone / Q000097:blood*; D005260:Female; D005438:Fludrocortisone / Q000009:adverse effects; D006801:Humans; D006929:Hyperaldosteronism / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D011188:Potassium / Q000097:blood; D012680:Sensitivity and Specificity; D012964:Sodium / Q000097:blood; D012965:Sodium Chloride / Q000008:administration & dosage*
D012965:Sodium Chloride; D000450:Aldosterone; D012964:Sodium; D011188:Potassium; D005438:Fludrocortisone